1. Field of the Invention
The present invention relates generally to a pneumatic cylinder, and more particularly to a compact self-chargeable pneumatic cylinder.
2. Background of the Invention
Pneumatic cylinders are used in various applications such as air springs, actuation devices, and exercise equipment. Conventional pneumatic cylinders generally comprise a hollow cylinder body, a piston disposed in the interior of the cylinder body, and a shaft coupled to the piston that extends out of the cylinder body.
Regardless of how a pneumatic cylinder is used, the gas chamber in the cylinder must be charged with a gas, such as atmospheric air, in order for the cylinder and piston arrangement to be operational. Various apparatuses and methods have been proposed wherein an external pump is used to charge the cylinder with a gas. However, in many situations, an external pump is not readily available due to the location of the cylinder, the mobility of the cylinder or the nature of the use. Furthermore, powered air pumps are only available in a very limited number of locations and manual pumps are burdensome to use and are often impractical to transport.
In the past, attempts have been made to provide a self-chargeable pneumatic cylinder wherein a manual pump mechanism is attached to the cylinder such that the device is not dependent on an external pump. However, each of these attempts has fallen short because the self-chargeable pneumatic cylinders that have been proposed heretofore involve a large number of components thereby making the cylinders expensive to manufacture and prone to mechanical failures. In addition, each of the existing self-chargeable pneumatic cylinders has a pump mechanism mounted on the exterior of the cylinder. This is a significant shortcoming because the external pump structure significantly increases the size of the cylinder and also detracts from the aesthetic appeal. Because of the bulkiness of these devices, in many applications, the external pump structure makes the pneumatic cylinder impractical for use due to spatial limitations. For these reasons, none of the proposed self-chargeable pneumatic cylinders has gained widespread acceptance.
The preferred embodiments of the present invention provide a new and improved self-chargeable pneumatic cylinder that does not require an external pump. The preferred embodiments also provide a self-chargeable pneumatic cylinder that is compact in size and has a rugged construction that ensures high quality and durability. Another feature of the preferred embodiments is that the self-chargeable pneumatic cylinder is well-suited for use as a pneumatic spring whereby the stiffness of the spring can be easily adjusted using the charging mechanism. The preferred embodiments are adapted to be made of a lightweight material that is resistant to corrosion. The preferred embodiments also provide a self-chargeable pneumatic cylinder that is very reliable, convenient to use and inexpensive to manufacture.
A significant feature of the self-chargeable pneumatic cylinder in accordance with the present invention is the location of the internal pump mechanism. The pump mechanism is substantially self-contained within the interior portion of the pneumatic cylinder and therefore does increase the overall dimensions of the device. In addition, because the pump mechanism is located internally, the components of the pump mechanism are well protected from damage.
In accordance with one aspect of the present invention, a pneumatic cylinder is presented generally comprising a hollow cylinder body having a closed end and an open end and a working piston slidably disposed in the interior of the cylinder body. A hollow elongate shaft is coupled to the working piston and extends out of the cylinder body via the open end. In a novel feature of the preferred embodiments of the present invention, the hollow interior portion of the shaft contains a manual pump mechanism. The manual pump mechanism generally comprises a pumping piston slidably disposed in the interior of the shaft and a pumping rod coupled to the pumping piston. The pumping rod is extendable out of the shaft via the open end and a handgrip is provided at the free end thereof for facilitating actuation of the pumping piston.
In another aspect of the present invention, the internal pump mechanism advantageously includes a check device disposed on the pumping piston. The check device comprises an annular slot formed in the periphery of the pumping piston and an O-ring disposed in the annular slot. The O-ring is in frictional engagement with the inner wall of the shaft at all times. Due to frictional forces, the O-ring is forced upward against the top of the annular slot as the pumping piston is retracted through the interior of the shaft. With the O-ring in this configuration, air is free to pass around the pumping piston into a pressure adding chamber. When the pumping piston is subsequently advanced back into the shaft, the O-ring presses against the bottom of the annular slot and forms a seal that prevents air from escaping the pressure adding chamber.
In another aspect of the present invention, a one-way valve is advantageously provided that extends through the working piston. The one-way valve allows air to flow in one direction only from the pressures adding chamber into the pressure cylinder to charge the cylinder with air as the pumping piston is actuated.
In another aspect of the present invention, the pneumatic cylinder is advantageously provided with a two-way valve disposed on the closed end of the cylinder body. The two-way valve provides an alternative means for rapidly charging the gas chamber in the cylinder. The two-way valve also provides a means to rapidly discharge the gas from the gas chamber to the atmosphere.
In another aspect of the preferred embodiments of the present invention, the shaft can be fully advanced into the cylinder after discharging all the gas from the cylinder. This feature can be used to reduce the size of the device for compact storage or transportation.
In another aspect of the present invention, the pneumatic cylinder is well adapted for use as a pneumatic spring in a pogo stick. The pressure in the gas chamber can be varied using the pump mechanism and/or the two-way valve to accommodate the body weight and skill level of the user. In this application, a buffer sleeve may be placed over the bottom end of the shaft to provide a foot for engagement with the ground during use. Because of the compact size of the pneumatic cylinder, the device is particularly well-suited for use with a pogo stick that is collapsible into a small volume.
In yet another aspect of the present invention, the pneumatic cylinder is well adapted for use with exercise equipment. The cylinder can be used with a wide variety of exercise machines wherein a resistance force is desirable. In this application, the resistance force can be adjusted to suit the user""s exercise needs by varying the pressure in the cylinder.